Well if we look at Euro release of iTunes store as a guide....
iTunes store launched April 2003 in USA
iTunes store launched June 2004 in the UK = 14 Months later
iTunes store launched January 2005 in Ireland = 18/19 Months later
I seriously hope iBookstore does not take this long to launch, but seeing as though they still have yet to even sort out licensing for films/tv/movies in many territories I wont be holding my breath.
iTunes however had no real competition at the time.
The only thing on our side is this...
Amazon's Kindle. We can already buy Kindle hardware from Amazon, but more importantly we can use the free Kindle App for the iPhone (and undoubtably an iPad enhanced version with page flips and nice enhanced GUI, and the same bookshelf idea Apple stole from Classics is already well in the works). Additionally we can already buy kindle books in $ pricing (saving more £ pounds & € euros) from it/web and read them on our iPhones/iPods without issue.
This alone may put some pressure on Apple, but as I say I am not optimistic. However if they do follow iTunes store timeline, in 12-18 months time most of us European iPad owners will be using Kindle and won't give a crap when iBookstore finally launches.